I'm not conscious of such function but maybe phpinfo(); may have some information on that?

Log pathways are defined inside apache site's configuration file, if you prefer a custom road to it otherwise automatically all of the logs are loaded into /var/log/apache2/*.log, so php do not have anything related to it

An interior server error has frequently something related to Apache and /var/log/httpd/ may be the error log file of apache, and so i think you're in the best file.